This invention relates to road surface condition detectors mounted on automotive vehicles for detecting the dry/wet condition of the driving road surface for the purpose of adjusting the parameters of the automatic control system of the suspensions and the brakes, etc, to ensure safety and enhance the reliability of the control system.
In the case of a conventional typical road surface condition detector, the dry/wet condition of the driving road surface is detected on the basis of the position of the wiper switch selected by the driver. Namely, when it rains during driving, the driver of the automotive vehicle turns on the wiper switch and selects a higher speed position thereof as the rain gets harder. Thus, the dry/wet condition of the road surface can be determined indirectly from the position of the wiper switch.
However, this method of determining the road surface condition is based on the driver's judgment, and hence is affected largely by the human inconsistency or the variation in the judgment of the respective individuals upon several occasions. Further, the wiper switch position selected by the driver does not necessarily agree with the dry/wet condition of the road surface. For example, when the rain stops, the wiper switch is turned off while the road surface is still wet. Hence, the information thus obtained is unreliable.
Thus, it has been proposed to dispose a sensor near a road wheel tire to detect the dry/wet condition of the road surface directly. Namely, the amount of the water, mud, sand, etc., splashed by the road wheel tire during driving time is detected by an impulse pressure sensor or a water amount sensor. This type of road surface condition detector is disclosed, for example, in Japanese Laid-Open Patent (Kokai) Nos. 61-98328 and 62-97836.
The road surface condition detector using a sensor disposed near a road wheel tire, however, has the following disadvantage. Namely, since the sensor is contaminated by the water, mud, sand, etc., which directly hits it, the device lacks durability. Thus the road surface condition detector can hardly be used in practical applications.